1. Field of the Invention
The present invention relates to a process for producing solid-state color image pickup array (hereinafter, shortened as solid-state color pickup array) having excellent performance characteristics.
2. Description of the Prior Art
For the production of solid-state image pickup element array provided with color-separating filters, viz. solid-state color pickup array, there has so far been known a process for the direct formation of color filters on a wafer having solid-state image pickup array. This direct formation process, known as a high precision and good yield method, includes a process utilizing vapor-deposited films of colorants such as dyes or pigments.
This process comprises repeating the following steps as many times as the number of colors necessary for the objective color filters: (1) formation of a film of colorant by vapor deposition on a wafer, (2) formation of a resist mask on the film, (3) formation of a pattern of color filters by wet etching with a selective solvent to dissolve the non-masked portion of the colorant film or by dry etching with a gas plasma or ions to ash the non-masked portion of the colorant film, and (4) formation of an intermediate transparent protective coating (the intermediate protective coating serves to protect the wafer and the already formed color filters from the etching in the next cycle).
The wet etching involves difficulties in selecting a solvent that dissolves the colorant alone without affecting the resist mask and in forming a fine structure for a color filter because the colorant film lying under the resist mask can hardly be protected from the attack of the solvent capable of dissolving the colorant.
None of these difficulties are found in the dry etching, which has, however, the following drawbacks.
The resist mask needs to be considerably thick because it also is removed during the etching of the non-masked portion of the colorant film, and the precision of the pattern is therefore lowered. In addition, the intermediate transparent protective coating is necessary for every color of the color filters in order to protect the wafer and the formed color filter elements from the dry etching. These protective coatings and the resist masks remain in the resulting filter, therefore they significantly decrease the transmittance of a formed color filter and increase the proportion of flare light. Furthermore, the whole color filter is inferior in heat resistance because of low heat resistances of the intermediate protective coatings and resist masks, although the colorant films themselves, being vapor-deposited, are excellent in heat resistance.